U.S. patent number RE37,725 [Application Number 09/454,170] was granted by the patent office on 2002-06-04 for radar apparatus for detecting a direction of a center of a target.
This patent grant is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Yukinori Yamada.
United States Patent |
RE37,725 |
Yamada |
June 4, 2002 |
Radar apparatus for detecting a direction of a center of a
target
Abstract
A radar apparatus of an automotive vehicle includes a radar unit
which radiates an electromagnetic wave to a target in a forward
direction of the vehicle and receives reflection beams from the
target to detect the target. A scanning control unit performs a
beam scanning of the radar unit to the target so that the
reflection beams during the beam scanning are received. A center
direction determining unit detects a distribution pattern of the
received reflection beams with respect to respective scanning
angles of the radar unit, performs a similarity approximation of
the distribution pattern by using an antenna directional gain
pattern of the radar unit to produce an approximated distribution
pattern, and determines a direction of a center of the target based
on a peak of the approximated distribution pattern.
Inventors: |
Yamada; Yukinori (Susono,
JP) |
Assignee: |
Toyota Jidosha Kabushiki Kaisha
(Toyota, JP)
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Family
ID: |
27337748 |
Appl.
No.: |
09/454,170 |
Filed: |
December 2, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
741206 |
Oct 29, 1996 |
05734344 |
Mar 31, 1998 |
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Foreign Application Priority Data
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Nov 10, 1995 [JP] |
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7-292580 |
Nov 24, 1995 [JP] |
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7-306278 |
Nov 24, 1995 [JP] |
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7-306279 |
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Current U.S.
Class: |
342/72;
342/107 |
Current CPC
Class: |
G01S
13/345 (20130101); G01S 13/424 (20130101); G01S
13/931 (20130101); G01S 7/032 (20130101); G01S
7/2883 (20210501); G01S 7/411 (20130101); G01S
2013/9319 (20200101); G01S 2013/93185 (20200101); G01S
13/42 (20130101); G01S 2013/932 (20200101) |
Current International
Class: |
G01S
13/93 (20060101); G01S 13/00 (20060101); G01S
13/34 (20060101); G01S 13/42 (20060101); G01S
7/03 (20060101); G01S 7/02 (20060101); G01S
7/41 (20060101); G01S 7/288 (20060101); G01S
7/285 (20060101); G01S 013/93 () |
Field of
Search: |
;342/70,71,72,147,107,108,109,110 ;340/903 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0568427 |
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Nov 1993 |
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EP |
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0611969 |
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Aug 1994 |
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EP |
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0658775 |
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Jun 1995 |
|
EP |
|
4-158293 |
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Jun 1992 |
|
JP |
|
6-148319 |
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May 1994 |
|
JP |
|
6-150195 |
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May 1994 |
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JP |
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6-242230 |
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Sep 1994 |
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JP |
|
7-5252 |
|
Jan 1995 |
|
JP |
|
7-49377 |
|
Feb 1995 |
|
JP |
|
7-63842 |
|
Mar 1995 |
|
JP |
|
7-242133 |
|
Sep 1995 |
|
JP |
|
Primary Examiner: Pihulic; Daniel T.
Attorney, Agent or Firm: Pillsbury Winthrop LLP
Claims
What is claimed is:
1. A radar apparatus of an automotive vehicle, comprising:
radar means for radiating an electromagnetic wave to a target in a
forward direction of the vehicle and for receiving reflection beams
from the target to detect the target;
scanning control means for performing a beam scanning of the radar
means to the target so that the reflection beams during the beam
scanning are received; and
center direction determining means for detecting a distribution
pattern of the received reflection beams with respect to respective
scanning angles of the radar means, for performing a similarity
approximation of the distribution pattern by using an antenna
directional gain pattern of the radar means to produce an
approximated distribution pattern, and for determining a direction
of a center of the target based on a peak of the approximated
distribution pattern.
2. The radar apparatus according to claim 1, further
comprising:
correcting means for determining a corrected center scanning angle
from a reference range value corresponding to a beam scanning range
of the radar means for a width of the target, and from a scanning
angle of the radar means corresponding to a mid-point of lower and
upper limits of the scanning angle in the distribution pattern,
when the vehicle is running along a curved path and the beam
scanning range is below the reference range value.
3. The radar apparatus according to claim 2, wherein said
correcting means includes:
means for detecting whether the vehicle is running along a curved
path, by comparing a radius of curvature of a present path along
which the vehicle is presently running with a predetermined
reference value, said radius of curvature being determined by using
a measured yaw rate and a measured vehicle speed.
4. The radar apparatus according to claim 2, wherein said
correcting means includes:
means for detecting whether a beam radiation axis of the radar
means directed to the target is slanting with respect to the
forward direction of the vehicle.
5. The radar apparatus according to claim 1, wherein, when the
vehicle is not running along a curved path, said center direction
determining means generates a signal indicating the direction of
the center of the target for a center scanning angle of the radar
means.
6. The radar apparatus according to claim 1, wherein, when a beam
radiation axis of the radar means directed to the target is not
slanting with respect to the forward direction of the vehicle, said
center direction determining means generates a signal indicating
the direction of the center of the target for a center scanning
angle of the radar means.
7. The radar apparatus according to claim 1, further
comprising:
alarm means for providing a warning of a dangerous condition of the
vehicle to a vehicle operator when the vehicle is detected to be in
the dangerous condition with respect to the target, based a
relative distance of the target and a relative velocity of the
target.
8. The radar apparatus according to claim 1, wherein said radar
apparatus includes a yaw rate sensor connected to an electronic
control unit, said yaw rate sensor measuring a yaw rate of the
vehicle and supplying the measured yaw rate to the electronic
control unit.
9. The radar apparatus according to claim 1, wherein said radar
apparatus includes a vehicle speed sensor connected to an
electronic control unit, said vehicle speed sensor measuring a
vehicle speed of the vehicle and supplying the measured vehicle
speed to the electronic control unit.
10. The radar apparatus according to claim 1, wherein said radar
means is a frequency-modulation-continuous-wave radar unit which
radiates an extremely-high-frequency electromagnetic
wave..Iadd.
11. A radar apparatus for an automotive vehicle in which a
radiation beam from a radar unit is transmitted to a target in a
forward direction of the vehicle and reflection beams from the
target are received so that a relative distance between the target
and the vehicle and a relative velocity of the target are detected
based on the reflection beams, said radar apparatus comprising:
a frequency modulation unit for modulating a frequency of a
radiation signal related to the radiation beam, in accordance with
a predetermined waveform;
a beat signal generating unit for generating a first beat signal
from the reflection beams during an up-period for which the
frequency of the radiation signal is increasing and a second beat
signal from the reflection beams during a down-period for which the
frequency of the radiation signal is decreasing;
a radar signal processing unit for determining spectrum level data,
including a first spectrum level of frequency of the first beat
signal and a second spectrum level of frequency of the second beat
signal, so that the relative distance and the relative velocity
related to the target are determined based on a pairing of a peak
in the first spectrum level and a peak in the second spectrum
level;
a scanning controller for performing a beam scanning of the radar
unit to the target with respect to a specific one of a plurality of
scanning ranges to that the reflection beams with respect to each
of the plurality of scanning ranges are received; and
a radar control unit for performing the pairing of the spectrum
level peaks for the spectrum level data from the radar signal
processing unit, based on the specific scanning range related to
the spectrum level peaks when two or more pairs of peaks in the
first spectrum level and in the second spectrum level, related to a
plurality of targets, are included in the spectrum level data for
the specific scanning range..Iaddend..Iadd.
12. The radar apparatus according to claim 11, wherein said radar
control unit makes a determination as to whether the pairing of the
spectrum level peaks for the spectrum level data is appropriately
performed, by comparing a correlation factor of the spectrum level
data related to the specific one of the plurality of scanning
ranges with a threshold value..Iaddend..Iadd.
13. The radar apparatus according to claim 12, wherein said radar
control unit stores the spectrum level data for the specific
scanning range into one of a plurality of predetermined areas of a
memory when it is determined that the correlation factor is not
above the threshold value..Iaddend..Iadd.
14. The radar apparatus according to claim 11, wherein, when the
spectrum level data is stored in one of a plurality of
predetermined areas of a memory, said radar control unit makes a
determination as to whether the spectrum level data has been fixed
to determine the relative distance and the relative velocity
related to a respective one of the plurality of
targets..Iaddend..Iadd.
15. The radar apparatus according to claim 11, wherein, when said
radar control unit has determined that the spectrum level data has
been fixed, said radar control unit makes a determination as to
whether the spectrum level peaks for the spectrum level data stored
in one of a plurality of predetermined areas of a memory are the
same as the spectrum level peaks for the spectrum level data stored
in an adjacent one of the plurality of predetermined
areas..Iaddend..Iadd.
16. The radar apparatus according to claim 11, wherein, when said
radar control unit has determined that the spectrum level peaks for
the spectrum level data stored in one of a plurality of
predetermined areas of a memory are the same as the spectrum level
peaks for the spectrum level data stored in an adjacent one of the
plurality of predetermined areas, said radar control unit performs
the pairing of the spectrum level peaks for the spectrum level data
stored in said one of the plurality of predetermined
areas..Iaddend..Iadd.
17. The radar apparatus according to claim 11, wherein said radar
control unit makes a determination as to whether two or more pairs
of peaks in the first spectrum level and in the second spectrum
level, related to the plurality of targets, are included in the
spectrum level data..Iaddend..Iadd.
18. The radar apparatus according to claim 11, wherein said radar
control unit determines values of the relative distance and the
relative velocity with respect to each of the plurality of targets
for the specific scanning range and stores the relative distance
values, the relative velocity values and the specific ranges of the
beam scanning related to each of the plurality of
targets..Iaddend..Iadd.
19. The radar apparatus according to claim 11, wherein said radar
apparatus includes a steering angle sensor connected to an
electronic control unit, said steering angle sensor outputting a
measured steering angle of the vehicle to the electronic control
unit..Iaddend..Iadd.
20. The radar apparatus according to claim 11, wherein said radar
apparatus includes a yaw rate sensor connected to an electronic
control unit, said yaw rate sensor outputting a signal indicating a
measured yaw rate of the vehicle to the electronic control
unit..Iaddend..Iadd.
21. The radar apparatus according to claim 11, wherein said radar
apparatus includes a vehicle speed sensor connected to an
electronic control unit, said vehicle speed sensor outputting a
signal indicating a measured speed of the vehicle to the electronic
control unit..Iaddend..Iadd.
22. The radar apparatus according to claim 11, wherein said radar
apparatus includes a frequency-modulation-continuous-wave radar
unit which radiates an extremely-high-frequency electromagnetic
wave as the radiation beam..Iaddend.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention generally relates to a scanning radar
apparatus, and more particularly to a scanning radar apparatus of
an automotive vehicle which detects a direction of a center of a
target, such as an advancing vehicle, by receiving reflection beams
from the target.
(2) Description of the Related Art
In recent years, several types of radar devices for use in
automotive vehicle have been developed in order to provide
increased stability and operability of the automotive vehicle. The
radar devices are capable of detecting a relative distance between
a target (such as an advancing vehicle) and the vehicle, and a
relative velocity of the target to a vehicle speed of the
vehicle.
Japanese Laid-Open Patent Application No. 4-158293 teaches a radar
apparatus which is one of the above-mentioned types. The radar
apparatus utilizes a radar unit radiating a laser beam in order to
detect a target such as an advancing vehicle in a forward direction
of the radar apparatus.
To make use of the radar apparatus of the above publication,
reflectors are mounted at a right-side rear end and a left-side
rear end of the advancing vehicle. The radar apparatus receives
reflection laser beams reflected off the reflectors of the
advancing vehicle (the target). The radar apparatus detects a
distance of each of the reflectors by measuring the time for the
radiation laser beam to return to the radar apparatus after it has
been reflected off the advancing vehicle. When the distances of the
reflectors are detected to be the same, the radar apparatus
determines a center scanning angle of the radar unit for a center
of the advancing vehicle by detecting a mid-point between two
scanning angles for the reflectors.
Another type is a radar apparatus utilizing a radar unit radiating
an extremely high frequency (EHF) electromagnetic wave in order to
detect the target. However, in a case of the radar apparatus of
this type, the radar apparatus receive reflection radar beams
containing noises from the reflectors of the advancing vehicle, and
the reflection of the radiation radar beam on the advancing vehicle
is not uniform.
It is difficult for the above-mentioned radar apparatus to
accurately detect a position of an end of the advancing vehicle by
measuring the time for the radiation radar beam to return to the
radar apparatus after it has been reflected off the advancing
vehicle. It is practically impossible for the above-mentioned radar
apparatus to determine a center scanning angle of the radar unit
for a center of the advancing vehicle by detecting a mid-point
between two scanning angles for the reflectors as in the laser-beam
radar apparatus.
Therefore, when the conventional radar apparatus utilizing the
radar unit radiating the EHF electromagnetic wave is used, it is
difficult to accurately detect the direction of the center of the
target.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved radar
apparatus in which the above-described problems are eliminated.
Another object of the present invention is to provide a radar
apparatus of an automotive vehicle which accurately detects a
direction of a center of a target in a forward direction of the
vehicle by performing a similarity approximation using an antenna
directional gain pattern of a radar unit.
Still another object of the present invention is to provide a radar
apparatus of an automotive vehicle which accurately detects
individual targets in a forward direction of the vehicle by
separately processing the data of received reflection signals
related to one target from the data related to another when a
plurality of adjacent targets are running in parallel in the
forward direction of the vehicle.
A further object of the present invention is to provide a radar
apparatus of an automotive vehicle which easily and accurately
detects individual targets in a forward direction of the vehicle by
separately performing a pairing of the data of received reflection
signals related to one target and a pairing of the data of received
reflection signals related to another target when a plurality of
targets in the forward direction of the vehicle are detected.
The above-mentioned objects of the present invention are achieved
by a radar apparatus which includes: a radar unit which radiates an
electromagnetic wave to a target in a forward direction of the
vehicle and receives reflection beams from the target to detect the
target; a scanning control unit which performs a beam scanning of
the radar unit to the target so that the reflection beams during
the beam scanning are received; and a center direction determining
unit which detects a distribution pattern of the received
reflection beams with respect to respective scanning angles of the
radar unit, performs a similarity approximation of the distribution
pattern by using an antenna directional gain pattern of the radar
unit to produce an approximated distribution pattern, and
determines a direction of a center of the target based on a peak of
the approximated distribution pattern.
The radar apparatus of the present invention can determine a
direction of a center of the target by performing the similarity
approximation even when the reflection of the radiation beam on the
target is not uniform and noises are superimposed in the received
reflection beams. Accordingly, it is possible for the radar
apparatus of the present invention to accurately detect the
direction of the center of the target for a center scanning angle
of the radar unit.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present invention
will become more apparent from the following detailed description
when read in conjunction with the accompanying drawings in
which:
FIGS. 1A and 1B are block diagrams showing basic concepts of the
present invention;
FIG. 2 is a block diagram of a radar apparatus in one embodiment of
the present invention;
FIG. 3 is a flowchart for explaining a center direction determining
procedure performed by the radar apparatus in FIG. 2;
FIG. 4 is a diagram showing a beam scanning of a radar unit to a
target which is performed by a radar scanning controller;
FIG. 5 is a diagram showing an ideal distribution pattern of
received reflection beams in which no noise is superimposed;
FIG. 6 is a diagram showing an actual distribution pattern of
received reflection beams in which noises are superimposed;
FIG. 7 is a diagram showing an antenna directional gain pattern
with respect to a scanning angle of the radar unit;
FIG. 8 is a diagram showing a similarity approximation of the
distribution pattern in FIG. 6 using the antenna directional gain
pattern in FIG. 7;
FIG. 9 is a diagram showing a case in which a vehicle is running
along a curved path and a target in the curve path is detected by
the radar unit;
FIGS. 10A, 10B and 10C are diagrams for explaining a correction of
a center scanning angle in the case of FIG. 9;
FIG. 11 is a block diagram of a radar apparatus in another
embodiment of the present invention;
FIG. 12 is a block diagram of a radar control unit of the radar
apparatus of FIG. 11;
FIG. 13 is a block diagram of a radar signal processing part of the
radar control unit in FIG. 12;
FIG. 14A is a diagram showing waveforms of radiation and reflection
signals of the radar signal processing part in FIG. 13;
FIG. 14B is a diagram showing waveforms of beat signals of the
radar signal processing part in FIG. 13;
FIG. 15A is a diagram showing a spectrum level of an up-frequency
determined by an FFT circuit in FIG. 13;
FIG. 15B is a diagram showing a spectrum level of a down-frequency
determined by the FFT circuit in FIG. 13;
FIG. 16 is a diagram showing a range of a beam scanning of the
radar unit in FIG. 11;
FIG. 17 is a diagram showing a relationship between a frequency of
a radiation signal and a scanning angle of the radar unit in FIG.
11;
FIG. 18 is a diagram showing a case in which two targets are
separately running with a distance along a straight path in a
forward direction of the vehicle;
FIG. 19 is a diagram showing data of received reflection signals in
the case of FIG. 18;
FIG. 20 is a diagram showing a case in which two adjacent targets
are running in parallel in a forward direction of the vehicle;
FIG. 21 is a diagram showing data of received reflection beams in
the case of FIG. 20;
FIG. 22 is a flowchart for explaining a control procedure performed
by the radar apparatus in FIG. 11;
FIG. 23 is a diagram showing a case in which the vehicle and the
target are separately running along a straight path with a relative
distance between the vehicle and the target;
FIG. 24 is a diagram showing a case in which the vehicle and the
target are running in the same lane along a curved path;
FIG. 25 is a block diagram of a radar apparatus in a further
embodiment of the present invention;
FIG. 26 is a diagram showing a beam scanning of the radar unit to
two separate targets in the forward direction of the vehicle;
FIGS. 27A and 27B are diagrams showing spectrum levels of an
up-frequency and a down-frequency determined for a range of the
beam scanning in FIG. 26;
FIGS. 28A and 28B, 29A and 29B, and 30A and 30B are diagram showing
spectrum levels of the up-frequency and the down-frequency
determined for other ranges of the beam scanning in FIG. 26;
and
FIGS. 31A and 31B are a flowchart for explaining a control
procedure performed by the radar apparatus in FIG. 25.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A description will now be given of the preferred embodiments of the
present invention with reference to the accompanying drawings.
FIG. 2 shows a radar apparatus in one embodiment of the present
invention. This radar apparatus is installed on an automotive
vehicle.
Referring to FIG. 2, the radar apparatus of the present embodiment
comprises a yaw rate sensor 10, an electronic control unit (ECU)
11, a radar scanning controller 12, a vehicle speed sensor 13 and a
radar unit 14. The radar apparatus of the present embodiment
further includes an alarm unit 15.
The yaw rate sensor 10 generates a yaw rate signal indicative of a
measured yaw rate of the vehicle by using an acceleration sensor
having a piezoelectric element, and supplies the yaw rate signal to
the ECU 11.
The vehicle speed sensor 13 generates a vehicle speed signal
indicative of a measured vehicle speed of the vehicle, and supplies
the vehicle speed signal to the ECU 11.
The ECU 11 receives the vehicle speed signal from the vehicle speed
sensor 13. The ECU 11 receives the yaw rate signal from the yaw
rate sensor 10. The ECU 11 performs a filtering of the received yaw
rate signal and determines a yaw rate signal after the filtering is
performed. The ECU 11 determines a measured radius of curvature of
a present path along which the vehicle is presently running, by
using the determined yaw rate signal and the vehicle speed
signal.
By using the measured radius of curvature of the present path, the
ECU 11 is capable of providing an estimated radius of curvature of
a following path along which the vehicle is about to run at a
following time.
Further, the ECU 11 generates a scanning angle signal indicative of
a scanning angle of the radar unit 14, and supplies the scanning
angle signal to the radar scanning controller 12. The radar unit 14
is controlled by the radar scanning controller 12 so that a beam
radiation axis of the radar unit 14 is moved to the target in
accordance with the scanning angle signal from the ECU 11.
Accordingly, the ECU 11 controls the radar unit 14 in accordance
with the scanning angle signal through the radar scanning
controller 12.
The radar unit 14 of the present embodiment is a
frequency-modulation-continuous-wave (FMCW) radar unit which
radiates an extremely high frequency (EHF) electromagnetic wave as
a radiation beam to a target in a forward direction of the vehicle.
A beam scanning of the radar unit 14 to the target is performed
under the control of the radar scanning controller 12 by moving the
radiation beam of the radar unit 14 across the target from the left
to the right of the target on the plane of a horizontal forward
running direction of the vehicle.
The radar unit 14 supplies signals indicative of results of the
detection of the target to the ECU 10. These signals are generated
by the radar unit 14 by receiving reflection beams after the
radiation beam has been reflected off the target. In response to
the signals from the radar unit 14, the ECU 10 is capable of
determining a relative distance between the target and the vehicle
and a relative velocity of the target relative to the vehicle speed
of the vehicle.
As described above, the ECU 11 determines, in response to the
received reflection beams, the relative distance and the relative
velocity related to the target. By using the relative distance and
the relative velocity, the ECU 11 detects whether the vehicle is in
a dangerous condition with respect to the target. When it is
determined that the vehicle is in a dangerous condition, the ECU 11
switches ON the alarm unit 15 in order to provide a warning of the
dangerous condition to a vehicle operator.
FIG. 3 shows a center direction determining procedure which is
executed by the ECU 11 of the radar apparatus in FIG. 2 by using
the yaw rate sensor 10, the vehicle speed sensor 13, the radar unit
14, and the radar scanning controller 12. This procedure is
repeatedly executed by the ECU 11 at intervals of a predetermined
time.
Referring to FIG. 3, the ECU 11, at step S10, allows the radar
scanning controller 12 to perform the beam scanning of the radar
unit 14 to the target. The beam scanning is performed under the
control of the radar scanning controller 12 by moving the radiation
beam of the radar unit 14 across the target from the left to the
right of the target on the plane of the horizontal forward running
direction of the vehicle.
The ECU 11, at step S12, detects a distribution pattern of received
reflection beams with respect to respective scanning angles
(.theta.) of the radar unit 14, based on the reflection beams
received from the target. When the relative distances and the
relative velocities related to the received reflection beams are
detected to be the same, the ECU 11 obtains a plotting of the
distribution pattern of the received reflection beams with respect
to the respective scanning angles of the radar unit 14.
FIG. 4 shows a beam scanning of the radar unit 14 to a target 20,
which is performed by the radar scanning controller 12. In FIG. 4,
the radar scanning controller 12 moves the radiation beam of the
radar unit 14 across the target 20 from the left to the right on
the plane of the horizontal forward running direction of the
vehicle. A scanning angle of the radar unit 14 is an angle between
a direction of the beam radiation axis of the radar unit 14 and the
horizontal forward running direction of the vehicle. This angle is
changed during the beam scanning.
During the beam scanning in FIG. 4, the beam radiation axis of the
radar unit 14 is moved relative to the forward running direction of
the vehicle across the target 20 from a left-side rear end of the
target 20 to a right-side rear end of the target 20. Detection of
the received reflection beams from the target 20 starts when the
beam radiation axis of the radar unit 14 is at a first scanning
angle .theta.1 for the left-side rear end, and the detection of the
received reflection beams ends when the beams radiation axis of the
radar unit 14 is at a second scanning angle .theta.2 for the
right-side rear end.
FIG. 5 shows an ideal distribution pattern of received reflection
beams in which no noise is superimposed. The distribution pattern
of the received reflection beams in FIG. 5 is obtained if the beam
scanning of the radar unit 14 is performed and the reflection of
the radiation beam on the target 20 is ideal. However, the limits
of a beam scanning range when detecting the target in an actual
case are not clear, and the reflection of the radiation beam on the
target in such a case is not uniform and it is complicated.
FIG. 6 shows an actual distribution pattern of received reflection
beams in which noises are superimposed. The distribution pattern of
the received reflection beams in FIG. 6 is obtained in an actual
case. As shown, the received reflection beams in the actual case
contains noises superimposed therein due to the non-uniform
reflection on the target.
Referring back to FIG. 3, after the step S12 is performed, step S14
performs a smoothing of the distribution pattern of the received
reflection beams. Influences of the noises in the actual
distribution pattern are reduced by this smoothing.
After the step S14 is performed, step S16 performs a similarity
approximation of the distribution pattern by using an antenna
directional gain pattern of the radar unit 14. FIG. 7 shows the
antenna directional gain pattern for the respective scanning angles
of the radar unit 14. FIG. 8 shows a similarity approximation of
the distribution pattern in FIG. 6 using the antenna directional
gain pattern in FIG. 7.
As shown in FIG. 8, when the similarity approximation is performed,
an approximated distribution pattern is produced from the
distribution pattern of the received reflection beams after the
smoothing, so that it is overlaid over the antenna directional gain
pattern. Respective correlations of the approximated distribution
pattern and the antenna directional gain pattern when the scanning
angle .theta. is changed from the first scanning angle .theta.1 for
the left-side rear end of the target 20 to the second scanning
angle .theta.2 for the right-side rear end of the target 20 are
calculated by the ECU 11.
After the step S16 is performed, step S18 determines a direction of
a center of the target 20 for a center scanning angle (.theta.c) of
the radar unit 14. As shown in FIG. 8, the direction of the center
of the target 20 is determined based on a peak of the approximated
distribution pattern. Based on the direction of the center of the
target 20, the ECU 10 generates a signal indicating the direction
of the center of the target 10 for the center scanning angle
(.theta.c) of the radar unit 14.
Even when the reflection of the radiation beam on the target is not
uniform and noises are superimposed in the received reflection
beams, a correspondence between the distribution pattern of the
received reflection beams and the antenna directional gain pattern
can be detected in the above manner.
Accordingly, the radar apparatus of the present embodiment can
determine the direction of the center of the target by performing
the above similarity approximation. It is possible for the radar
apparatus of the present embodiment to accurately detect the
direction of the center of the target for the center scanning angle
.theta.c of the radar unit.
After the step S18 is performed, step S20 detects whether the
vehicle is presently running along a curved path. The ECU 11
determines a radius (R1) of curvature of a present path along which
the vehicle is presently running, by using a measured yaw rate
signal (YAW) from the yaw rate sensor 10 and a measured vehicle
speed signal (SPD) from the vehicle speed sensor 12. The radius R1
of curvature of the present path is determined in accordance with
the equation: R1=SPD/YAW. That is, the radius R1 of curvature of
the present path is calculated by dividing the measured vehicle
speed SPD by the measured yaw rate YAW. By comparing the determined
radius R1 of curvature of the present path with a predetermined
reference value, the ECU 11 detects whether the vehicle is
presently running along a curved path.
When the radius R1 of curvature of the present path is above the
predetermined reference value, it is determined that the vehicle is
not presently running along a curved path. At this time, the ECU 11
generates a signal indicating the determined center scanning angle
.theta.c (the step S18) in order to detect a direction of the
center of the target. Further, steps S26 and S28 which will be
described later are performed by the ECU 11. The center direction
determining procedure in FIG. 3 ends after the steps S26 and S28
are performed.
On the other hand, when the radius R1 of curvature of the present
path is below the predetermined reference value, it is determined
that the vehicle is presently running along a curved path.
When the result at the step S20 is affirmative (the vehicle is
presently running along a curved path), step S22 is performed by
the ECU 11. Step S22 detects whether a beam scanning range .theta.w
of the target is below a reference range value (=2.theta.vh). This
discrimination is made to determine whether the beam radiation axis
of the radar unit 14 directed to the target when the center
scanning angle is determined at the step S18 is excessively
slanting with respect to the horizontal forward running direction
of the vehicle.
The ECU 11 at the step S22 determines the beam scanning range
.theta.w of the target by a difference between a lower limit of the
scanning angle in the level of the received reflection beams which
is above a threshold value and an upper limit of the scanning angle
.delta. in the level of the received reflection beams which is
above the threshold value.
The above reference range value 2.theta.vh is determined by the
following equation.
where L is the measured relative distance of the target and W is a
width of the target. The width W of the target (the advancing
vehicle) in the present case is about 2 meter. According to the
above equation, the value of .theta.vh, or 1/2 of the reference
range value, corresponds to a beam scanning range of the radar unit
14 for 1/2 of the width of the advancing vehicle.
FIG. 9 shows a case in which a vehicle 25 is running along a curved
path and a target 30 in the curve path is detected by the radar
apparatus of the vehicle 25.
In the case of FIG. 9, the beam radiation axis of the radar unit 14
directed to the target 30 is excessively slanting with respect to
the horizontal forward running direction of the vehicle. FIG. 10A
shows a distribution pattern of received reflection beams obtained
in the slanting case of FIG. 9. The level of the received
reflection beams in the slanting case of FIG. 9 is the maximum when
the beam radiation axis of the radar unit 14 is directed to the
left-side rear end of the target 30 as shown in FIG. 10A.
FIG. 10B shows a distribution pattern of received reflection beams
obtained in a normal case in which the beam radiation axis of the
radar unit 14 directed to the target 30 accords with the horizontal
forward running direction of the vehicle.
As shown, a beam scanning range .theta.w1 of the target 30 in the
slanting case of FIG. 10A is smaller than a beam scanning range
.theta.w2 in the normal case of FIG. 10B. The above reference range
value 2.theta.vh used at the step S22 is defined by an estimated
value of the beam scanning range .theta.w2 in the normal case.
Accordingly, when the vehicle 25 is running along the curved path
and the beam scanning range .theta.w of the target is below the
reference range value 2.theta.vh, it is necessary to correct the
center scanning angle .theta.c determined at the step S18.
When the result at the step S22 is affirmative
(.theta.w.ltoreq.2.theta.vh), step S24 is performed by the ECU 11.
Step S24 determines a corrected center scanning angle .theta.c so
as to eliminate an offset of the center scanning angle .theta.c
which is produced at the step S18 in the slanting case.
FIG. 10C shows a correction of a center scanning angle in the case
of FIG. 9. As shown in FIG. 10C, the corrected center scanning
angle .theta.c is calculated by addition of a tentatively
determined center scanning angle for the mid-point of the lower
limit "A1" and the upper limit "A2" and the value of .theta.vh
(which is equal to 1/2 of the reference range value corresponding
to the beam scanning range of the radar unit 14 for 1/2 of the
width of the target). That is, the corrected center scanning angle
.theta.c in the case of FIG. 9 is determined at the step S24 by the
following equation.
where A1 is the lower limit of the scanning angle, A2 is the upper
limit of the scanning angle, and .theta.vh is equal to 1/2 of the
reference range value of the radar unit 14.
Referring back to FIG. 3, after the step S24 is performed, step S26
is performed by the ECU 11.
On the other hand, when the result at the step S22 is negative
(.theta.w>2.theta.vh), the step S26 is performed and the step
S24 (the correction of the center scanning angle) is not performed.
At this time, the ECU 11 generates a signal indicating the
determined center scanning angle .theta.c (the step S18) in order
to detect a direction of the center of the target.
As described above, when the vehicle is running along a curved path
and the beam radiation axis of the radar unit directed to the
target is slanting with respect to the forward direction of the
vehicle, the radar apparatus of the present embodiment can
eliminate the offset of the center scanning angle .theta.c which is
determined in the slanting case. Accordingly, it is possible for
the present embodiment to accurately detect the center scanning
angle .theta.c of the radar unit for the center of the target in
the slanting case also.
Step S26 detects whether the center scanning angle .theta.c, which
is determined at the step S18 or the step S24, meets the following
conditions.
where .theta.cv is a center scanning angle for a center of a
roadway lane of the vehicle, L is the measured relative distance of
the target, and R1 is the radius of curvature of the present path.
When the above conditions are met by the center scanning angle
.theta.c, it is determined that the target is in the roadway lane
which is the same as that of the vehicle.
After the step S26 is performed, step S28 is performed by the ECU
11. Step S28 detects whether the vehicle is in a dangerous
condition with respect to the target, by receiving the relative
distance and the relative velocity related to the target. When it
is determined that the vehicle is in a dangerous condition, the ECU
11 switches ON the alarm unit 15 in order to provide a warning of
the dangerous condition to a vehicle operator. After the step S28
is performed, the center direction determining procedure in FIG. 3
ends.
FIG. 1A shows a radar apparatus according to a basic concept of the
present invention. The basic concept of the present invention is
already apparent from the foregoing description of the above
embodiment. As shown in FIG. 1A, the radar apparatus includes a
radar unit 16, a scanning control unit 17, and a center direction
determining unit 18.
The radar unit 16 is constructed by the radar unit 14 of the
above-described embodiment in FIG. 2. The radar unit 16 radiates an
electromagnetic wave to a target in a forward direction of a
vehicle and receives reflection beams from the target to detect the
target.
The scanning control unit 17 is constructed by the radar scanning
controller 12 of the above embodiment in FIG. 2 and the step S10 of
the center direction determining procedure executed by the ECU 11.
The scanning control unit 17 performs a beam scanning of the radar
unit 16 to the target so that the reflection beams during the beam
scanning are received.
The center direction determining unit 18 is constructed by the
steps S12 through S18 in the center direction determining procedure
executed by the ECU 11. The center direction determining unit 18
detects a distribution pattern of the received reflection beams
with respect to respective scanning angles of the radar unit 16.
The determining unit 18 performs a similarity approximation of the
distribution pattern by using an antenna directional gain pattern
of the radar unit 16 to produce an approximated distribution
pattern. The determining unit 18 determines a center scanning angle
of the radar unit 16 for a center of the target by a scanning angle
of the approximated distribution pattern corresponding to a peak of
the antenna directional gain pattern.
Further, FIG. 1B shows a radar apparatus according to another basic
concept of the present invention. This basic concept of the
invention is also apparent from the foregoing description of the
above embodiment. As shown in FIG. 1B, this radar apparatus
includes a correcting unit 19 in addition to the units 16, 17 and
18 in FIG. 1A. In FIG. 1B, the elements which are the same as
corresponding elements in FIG. 1A are designated by the same
reference numerals, and a description thereof will be omitted.
Referring to FIG. 1B, the correcting unit 19 is constructed by the
steps S20 through S24 in the center direction determining procedure
executed by the ECU 11. The correcting unit 19 determines a
corrected center scanning angle from a reference range value
corresponding to a beam scanning range of the radar unit 16 for a
width of the target, and from a scanning angle of the radar unit 16
corresponding to a mid-point of lower and upper limits of the
scanning angle in the distribution pattern, when the vehicle is
running along a curved path and the beam scanning range is below
the reference range value.
Further, the correcting unit 19 in FIG. 1B includes a unit for
detecting whether the vehicle is running along a curved path, by
comparing a radius of curvature of a present path along which the
vehicle is presently running with a predetermined reference value.
The radius of curvature is determined by using a measured yaw rate
and a measured vehicle speed.
Further, the correcting unit 19 includes a unit for detecting
whether a beam radiation axis of the radar unit 16 directed to the
target is slanting with respect to the forward direction of the
vehicle.
Next, FIG. 11 shows a radar apparatus in another embodiment of the
present invention.
Referring to FIG. 11, the radar apparatus is controlled by a radar
control unit 110 and a vehicle control unit 112 which are two
separate electronic control units (ECU). This radar apparatus is
installed on an automotive vehicle.
A steering angle sensor 114, a yaw rate sensor 116, and a vehicle
speed sensor 118 are connected to inputs of the radar control unit
(ECU) 110. The steering angle sensor 114 generates a signal
indicative of a steering angle of a steering wheel (not shown) of
the vehicle. The yaw rate sensor 116 generates a signal
proportional to an angular velocity of the vehicle about a center
of gravity of the vehicle. The vehicle speed sensor 118 generates a
signal indicative of a vehicle speed of the vehicle.
The radar control unit (ECU) 110 is capable of providing an
estimated radius of a turning circle of the vehicle by receiving
these signals from the steering angle sensor 114, the yaw rate
sensor 116 and the vehicle speed sensor 118.
A radar unit 120 is connected to an input of the radar control unit
110. An output of the radar control unit 110 is connected to a
scanning controller 122.
The radar unit 120 of the present embodiment is a
frequency-modulation-continuous-wave (FMCW) radar unit which
radiates an extremely high 10 frequency (EHF) electromagnetic wave
as the radiation beam to a target in a forward direction of the
vehicle. The radar unit 120 has a rotating shaft 120a on which an
antenna of the radar unit 120 is rotatably supported. By rotating
the radar unit 120 on the rotating shaft 120a, the beam radiation
axis of the radar unit 120 is changed.
A moving mechanism 124 is engaged with the radar unit 120 to move
the beam radiation axis of the radar unit 120. The operation of the
moving mechanism 124 is performed by the scanning controller 122
through a feedback control. A scanning angle signal (.theta.)
output from the radar control unit 110 is supplied to the scanning
controller 122. The scanning controller 122 feedback-controls the
moving mechanism 124 to move the beam radiation axis of the radar
unit 120 so that a scanning angle of the radar unit 120 is adjusted
to be in accordance with a scanning angle indicated by the scanning
angle signal (.theta.).
The radar control unit 110 controls a beam scanning of the radar
unit 120 to the target through the scanning controller 122 by
increasing or decreasing the scanning angle (.theta.) at a given
period of time. By moving the radiation beam of the radar unit 120
across the target from the left to the right of the target on the
plane of the horizontal forward running direction of the vehicle,
the beam scanning of the radar unit 120 is carried out.
Signals related to the received reflection beams from the target
are supplied from the radar unit 120 to the radar control unit 110.
In response to these signals, the radar control unit (ECU) 110
detects the target in the forward direction of the vehicle. The
results of the detection of the target are supplied from the radar
control unit 110 to the vehicle control unit (ECU) 112.
An alarm unit 126, a brake unit 128, and a throttle valve 130 are
connected to outputs of the vehicle control unit 112. When the
vehicle is detected to be in a dangerous condition with respect the
target, the vehicle control unit 112 switches ON the alarm unit
126, controls the brake unit 128, and/or controls the throttle
valve 130, in order to provide a warning of the dangerous condition
to a vehicle operator and decelerate the vehicle for safety.
FIG. 12 shows a construction of the radar control unit (ECU) 110 of
the radar apparatus in FIG. 11.
The radar control unit 110 is essentially made up of a
microcomputer. As shown in FIG. 12, the radar control unit 110
comprises a scanning angle determining part 132, a radar signal
processing part 134, and a target recognition part 136.
The scanning angle determining part 132 determines a scanning angle
of the radar unit 120, and supplies a scanning angle signal
indicating the scanning angle to the scanning controller 122 as
described above. In the scanning angle determining part 132, the
scanning angle (.theta.) indicated by the supplied scanning angle
signal is changed in synchronism with a control timing of the radar
signal processing part 134.
When any target is detected as a result of the beam scanning of the
radar unit 120, the radar signal processing part 134 receives
signals of the reflection beams of the target from the radar unit
120. In response to these signals, the radar signal processing part
134 determines a relative distance between the target and the and
the vehicle and a relative velocity of the target to the vehicle
speed of the vehicle. Data of the relative distance and the
relative velocity related to each of a plurality of targets, and
correlations between such data and respective scanning angles with
respect to each of the targets are generated by the radar signal
processing part 134, and they are supplied to the target
recognition part 136. A construction of the radar signal processing
part 134 will be described later with reference to FIG. 13.
When the relative distances, the relative velocities, and the
correlations for the respective targets from the radar signal
processing part 134 are received, the target recognition part 136
generates a set of groups of recognition data, each group of the
recognition data related to the relative distance, the relative
velocity and the correlations of the same target. The target
recognition part 136 provides an estimated radius (R) of the
turning circle of the vehicle based on the signals output from the
steering angle sensor 114, the yaw rate sensor 116 and the vehicle
speed sensor 118, as described above.
The radar apparatus of the present embodiment is characterized by
the target recognition part 136 which separately generates each of
groups of the recognition data of the relative distances, the
relative velocities, and the correlations to the respective
scanning angles, by using the estimated radius (R) of the turning
circle of the vehicle, which are separated from each other for one
of the targets being detected.
FIG. 13 shows a construction of the radar signal processing part
134 in FIG. 12. As shown in FIG. 13, a radiation antenna 120b and a
receiving antenna 120c are included in the radar unit 120. The
radar signal processing part 134 comprises a carrier generator 138,
frequency modulation circuit 140, a modulation voltage generator
142, and a directional coupler 144. These elements constitute a
beam radiation portion of the FMCW radar unit. An output of the
directional coupler 144 is connected to the radiation antenna 120b
of the radar unit 120.
The carrier generator 138 generates a carrier signal having a given
frequency, and supplies this signal to the frequency modulation
circuit 140.
The modulation voltage generator 142 generates a modulation signal
whose amplitude is varied in a triangular form, and supplies this
signal to the frequency modulation circuit 140.
The frequency modulation circuit 140 performs a frequency
modulation of the carrier signal output from the carrier generator
138 in accordance with the triangular-form modulation signal output
from the modulation voltage generator 142. Thus, a modulated signal
is generated at an output of the frequency modulation circuit
140.
FIG. 14A shows waveforms of radiation and reflection signals of the
radar signal processing part 134 in FIG. 13. The waveform of the
radiation signal indicated by a solid line in FIG. 14A shows a
change in the frequency of the modulated signal at the output of
the frequency modulation circuit 140. At a result of the
above-mentioned frequency modulation, the modulated signal is
generated at the output of the frequency modulation circuit
140.
As shown in FIG. 14A, the frequency of this modulated signal (the
radiation signal) is varied in a triangular form. A frequency
change width of the radiation signal is indicated by "dF", and a
modulation frequency of the radiation signal is indicated by "fm"
(fm=1/T where T is a period of the amplitude change of the signal
output by the modulation voltage generator 142). The modulated
signal output from the frequency modulation circuit 140 is supplied
to the radiation antenna 120b via the directional coupler 144, and
this signal is supplied to a mixer 146 (which will be described
later) via the directional coupler 144.
The radiation signal (the above modulated signal) supplied to the
radiation antenna 120b is radiated as the radiation beams by the
radar unit 120 to a target in a forward direction of the vehicle in
accordance with the scanning angle signal (.theta.). When there is
the target in the forward direction of the vehicle, reflection
signals which are reflection beams after the radiation beam has
been reflected off the target are received at the receiving antenna
120c of the radar unit 120.
The receiving antenna 120c is connected to an input of the mixer
146. The radar signal processing part 134 comprises the mixer 146,
an amplifier 148, a filter 150, and a fast-Fourier-transform (FFT)
circuit 152. These elements and the radar unit 120 constitute a
beam receiving portion of the FMCW radar unit. In response to the
reflection signals supplied from the receiving antenna 120c, the
radar signal processing part 134 generates the data of the relative
distance and the relative velocity related to the target, through
the radar signal processing.
The waveforms of reflection signals indicated by a dotted line and
a one-dot chain line in FIG. 14A show changes of the frequencies of
the reflection signals supplied from the receiving antenna 120c to
the mixer 146.
The mixer 146 performs a mixing of the radiation signal from the
directional coupler 144 and the reflection signals from the
receiving antenna 120c, and generates beat signals at an output of
the mixer 146 as a result of the mixing. Changes of the frequencies
of the beat signals at the output of the mixer 146 are in
accordance with the differences between the radiation signal
frequency and the reflection signal frequencies.
FIG. 14B shows waveforms of the beat signals generated in the radar
signal processing part 134 in FIG. 13. Hereinafter, as shown in
FIGS. 14A and 14B, a frequency of a beat signal generated at an "up
period" during which the frequency of the radiation signal is
increasing is called an up-frequency "fup", and a frequency of a
beat signal generated at a "down period" during which the frequency
of the radiation signal is decreasing is called a down-frequency
"fdwn".
The beat signals generated at the output of the mixer 146 are
supplied to the filter 150 after they have been amplified by the
amplifier 148. The beat signals from the amplifier 148 are
separated by the filter 150 into the beat signals of the up periods
and the beat signals of the down periods. These beat signals at the
output of the filter 150 are separately supplied to the FFT circuit
152.
Thus, the FFT circuit 152 determines a power spectrum of the
up-frequency for the beat signals of the up periods through the
fast Fourier transform, and determines a power spectrum of the
down-frequency for the beat signals of the down periods through the
fast Fourier transform.
FIG. 15A shows the spectrum level of the up-frequency determined by
the FFT circuit 152 for the beat signals of the up periods when two
targets in the scanning range of the radar unit 120 are detected.
FIG. 15B shows the spectrum level of the down-frequency determined
by the FFT circuit 152 for the beat signals of the down periods in
the same case.
In a case in which there are a plurality of targets in the scanning
range of the radar unit 120, different reflection signals from the
individual targets are received at the receiving antenna 120c.
Different beat signals for the respective reflection signals of the
targets are generated at the output of the mixer 146. Consequently,
the spectrum level of the up-frequency determined by the FFT
circuit 152 has a plurality of peaks, such as "FMu1" and "FMu2" in
FIG. 15A, and the spectrum level of the down-frequency determined
by the FFT circuit 152 has a plurality of peaks, such as "FMd1" and
"FMd2" in FIG. 15B.
Generally, there is a phase difference between the radiation signal
output by the radiation antenna 120b and the reflection signal
received by the receiving antenna 120c, and this phase difference
is proportional to the time for the signals to be transmitted over
the distance between the vehicle and the target.
When the relative velocity of the target is zero (the speed of the
target is equal to the vehicle speed of the vehicle), no Doppler
shift of the frequency of the reflection signal takes place. The
waveform of the reflection signal in this case which shows the
change of the frequency of the reflection signal supplied to the
mixer 146 is as indicated by the one-dot chain line in FIG. 14A. As
shown, the waveform of the reflection signal in this case (the
one-dot chain line) is described by translating the waveform of the
radiation signal (the solid line) in a direction parallel to the
time axis "t".
Therefore, when the relative velocity of the target is zero, the
up-frequency fup of the beat signal is the same as the
down-frequency fdwn of the beat signal (fup=fdwn), which is
indicated by the one-dot chain line in FIG. 14B. Each value of the
up-frequency fup and the down-frequency fdwn in the present case is
proportional to the relative distance between the target and the
vehicle.
On the other hand, when the relative velocity (Vr) of the target is
greater or smaller than zero (the target moves away from the
vehicle or the vehicle approaches the target), a Doppler shift of
the frequency of the reflection signal proportional to the relative
velocity Vr takes place. For example, when the relative velocity Vr
is smaller than zero, the frequency of the reflection signal in
this case is shifted to a frequency higher than the frequency of
the radiation signal due to the Doppler shift.
Since the Doppler shift occurs in the present case, the waveform of
the reflection signal which shows the change of the frequency of
the reflection signal supplied to the mixer 146 is that indicated
by the dotted line in FIG. 14A. As shown, the waveform of the
reflection signal in this case (the dotted line) is described by
translating the waveform of the radiation signal (the solid line)
both in a direction parallel to the time axis "t" and in a
direction parallel to the frequency axis "f".
When the relative velocity Vr is smaller than zero and the
frequency of the reflection signal is shifted to the higher
frequency as in FIG. 14A, the up-frequency fup of the beat signal
is reduced and the down-frequency fdwn of the beat signal is
enlarged, which is indicated by the dotted line in FIG. 14B. Each
value of the up-frequency fup and the down-frequency fdwn in the
present case contains a Doppler shift component which is
superimposed in the beat signal.
In the present case, an average of the up-frequency and the
down-frequency is determined by
By obtaining the average fr by the above Equation (1), the Doppler
shift components of the up-frequency fup and the down-frequency
fdwn in the average fr are canceled by each other. It is possible
to obtain the average fr of the up-frequency and the down-frequency
which is proportional to the relative distance between the target
and the vehicle since it contains no Doppler shift component.
Further, in the present case, a value fd of 1/2 of a difference
between the up-frequency fup and the down-frequency fdwn is
determined by
By obtaining the value fd by the above Equation (2), an average of
the sum of the Doppler shift components of the up-frequency fup and
the down-frequency fdwn is determined. It is possible to obtain the
value fd which is equivalent to the Doppler shift component of each
of the up-frequency and the down-frequency due to the relative
velocity of the target.
In the present embodiment, the following relationships are met,
supposing that a target in the scanning range of the radar unit 120
is detected, the relative distance of the target being indicated by
L, and the relative velocity of the target being indicated by
Vr.
where fo is a central frequency of the modulation signal output by
the modulation voltage generator 142, fm is a frequency of the
modulated signal output by the frequency modulation circuit 140, dF
is the frequency change width of the modulated signal, and c is the
travel speed of the electromagnetic wave.
Therefore, if the peaks of the spectrum levels of the up-frequency
and the down-frequency of the beat signals are determined by the
FFT circuit 152, the values of the "fr" and the "fd" can be
obtained by using the above Equations (1) and (2). Further, the
values of the relative distance L and the relative velocity Vr
related to the target can be obtained by substituting the values of
the "fr" and the "fd" into the above Equations (3) and (4).
As described above, the moving mechanism 124 is feedback-controlled
by the scanning controller 122 to move the beam radiation axis of
the radar unit 120, so that the scanning angle of the radar unit
120 is adjusted to be in accordance with the scanning angle signal
(.theta.) output from the radar control unit 110.
FIG. 16 shows a range of the beam scanning of the radar unit 120,
which is predetermined on a vehicle 54 in which the radar apparatus
of the present embodiment in FIG. 11 is incorporated.
Referring to FIG. 16, when the beam scanning of the radar unit 120
to the target is performed, the radiation beam of the radar unit
120 is moved by the scanning controller 122 across the target from
the left to the right or vice versa on the plane of the horizontal
forward running direction of the vehicle 54. As described above,
the scanning angle (.theta.) of the radar unit 120 is the angle
between the direction of the beam radiation axis of the radar unit
120 and the horizontal forward running direction of the vehicle 54.
As shown in FIG. 16, the scanning angle (.theta.) is changed from
-10.degree. to +10.degree. or vice versa during the beam scanning
of the radar unit 120, and the horizontal forward running direction
of the vehicle 54 accords with the direction of the scanning angle
0.degree.. The scanning angle .theta. is negative (or smaller than
zero) when the radiation beam of the radar unit 120 covers a range
on the left side of the target, and the scanning angle .theta. is
positive (or greater than zero) when the radiation beam of the
radar unit 120 covers a range on the right side of the target.
FIG. 17 shows a relationship between the frequency f of the
radiation signal and the scanning angle .theta. of the radar unit
120 in FIG. 11. As described above, the scanning angle .theta.
supplied by the scanning angle determining part 132 is changed in
synchronism with the control timing of the radar signal processing
part 134.
More specifically, in the radar apparatus of the present
embodiment, the scanning angle .theta. is changed by 0.5.degree.
when the frequency f of the radiation signal is changed for one
period. In addition, in the radar apparatus of the present
embodiment, the beam scanning of the radar unit 120 during which
the scanning angle .theta. is changed from -10.degree. to
+10.degree. or vice versa is repetitively performed for every 100
milliseconds (msec).
In the radar control unit 110 of the present embodiment, the
calculations of the values of the "fr" and the "fd" using the above
Equations (1) and (2) and the calculations of the values of the
relative distance L and the relative velocity Vr related to the
target by using the values of the "fr" and the "fd" and the above
Equations (3) and (4) are repetitively carried out each time the
scanning angle .theta. is changed by 0.5.degree. for every 2.5
msec. Also, the beam scanning of the radar unit 120 is repetitively
carried out through the scanning controller 122 each time the
scanning angle .theta. is changed by 0.5.degree..
Accordingly, in the present embodiment, the range of the beam
scanning of the radar unit 120 in FIG. 16 (in which the scanning
angle .theta. is changed from -10.degree. to +10.degree.) is
divided into forty subsections, the calculated values of the "fr"
and the "fd" and the calculated values of the relative distance L
and the relative velocity Vr related to the target are obtained for
each subsection (corresponding to 2.5 msec) of the beam scanning of
the radar unit 120. Thus, in the present embodiment, for every 100
msec during which the beam scanning of the radar unit 120 to the
target is completed, forty sets of the peaks of the spectrum levels
of the up-frequency and the down-frequency (as in FIGS. 15A and
15B), corresponding to respective forty scanning angles .theta.,
are determined by the FFT circuit 152, and forty sets of the
calculated values of the "fr" and the "fd" and the calculated
values of the relative distance L and the relative velocity Vr
related to the target, corresponding to the respective forty sets
of the peaks, are obtained by the radar signal processing part 134.
These calculated values which are related to the respective
scanning angles .theta. are supplied from the radar signal
processing part 134 to the target recognition part 136.
FIG. 18 shows a case in which two targets T1 and T2 (which are
advancing vehicles) are separately running with a distance along a
straight path in a forward direction of the vehicle 54. In FIG. 18,
the target T1 is running forwardly in a roadway lane which is the
same as a roadway lane of the vehicle 54. The target T2 is running
forwardly in a roadway lane which is different from and adjacent to
the roadway lane of the vehicle 54, and the target T2 is advancing
forward from the target T1.
FIG. 19 shows data of received reflection signals at the input of
the target recognition part 136 of the radar apparatus on the
vehicle 54, in the case of FIG. 18. The data of the received
reflection signals in FIG. 19 includes a plurality of plots of the
relationship between the scanning angle (.theta.) and the relative
distance (L) related to each of the target T1 and the target
T2.
As shown in FIG. 19, a group of plots of the data of the received
reflection signals related to the target T2 gathers in an area in
which the relative distance L is large. A different group of plots
of the data of the received reflection signals related to the
target T1 gathers in a separate area in which the relative distance
L is small. In the present case, as shown in FIG. 19, it is
possible to easily distinguish the group of the plots related to
the target T2 and the group of the plots related to the target T1
with respect to each of the relative distance L and the relative
velocity Vr.
FIG. 20 shows a case in which two adjacent targets T1 and T2 (which
are advancing vehicles) are running in parallel along a straight
path in the forward direction of the vehicle 54. There is no
substantial distance between the target T1 and the target T2 along
the straight path. In FIG. 20, the target T1 is running forwardly
in the roadway lane which is the same as the roadway lane of the
vehicle 54. The target T2 is running forwardly in the adjacent
roadway lane which is different from to the roadway lane of the
vehicle 54. In the present case, the target T1 and the target T2
are advancing in parallel forward from the vehicle 54.
FIG. 21 shows data of received reflection beams at the input of the
target recognition part 136 of the radar apparatus on the vehicle
54, in the case of FIG. 20. The data of the received reflection
signals in FIG. 21 includes a plurality of plots of the
relationship between the scanning angle (.theta.) and the relative
distance (L) related to both the target T1 and the target T2.
As shown in FIG. 21, a group of plots of the data of the received
reflection signals related to the target T2 and a group of plots of
the data of the received reflection signals related to the target
T1 gather in a single area in which the respective relative
distances L are substantially the same. In the present case, as
shown in FIG. 21, it is difficult to distinguish the group of the
plots related to the target T2 and the group of the plots related
to the target T1 with respect to each of the relative distance L
and the relative velocity Vr.
The radar apparatus of the present embodiment is characterized by
the target recognition part 136 which allows the radar control unit
110 to easily distinguish the group of the recognition data related
to the target T2 and the group of the recognition data related to
the target T1 with respect to each of the relative distance L and
the relative velocity Vr, even in the case of FIGS. 20 and 21.
FIG. 22 shows a control procedure performed by the target
recognition part 136 of the radar control unit (ECU) 110 in FIG.
12. This control procedure is performed in order to achieve the
above-mentioned function of the target recognition part 136. The
control procedure in FIG. 22 is started for every 100 msec needed
for one beam scanning of the radar unit 120 to be performed by
changing the scanning angle .theta. from -10.degree. to +10.degree.
or vice versa.
When the control procedure in FIG. 22 is started, the target
recognition part 136 of the ECU 110, at step S40, detects whether a
target in the roadway lane which is the same as that of the vehicle
54 has been detected at a preceding cycle of the control
procedure.
The radar apparatus of the present embodiment can determine the
relative distance L of the target to the vehicle 56 if a target in
the scanning range of the radar unit 120 in the forward direction
of the vehicle 56 is detected. The determination as to whether the
target is in the roadway lane which is the same as that of the
vehicle 54 is performed at the step S40 as follows.
FIG. 23 shows a scanning range of the radar unit 120 when the
vehicle 54 and a target 56 are separately running along a straight
path with a relative distance L between the vehicle 54 and the
target 56. If the forward direction of the target 56 accords with
the forward direction of the vehicle 54, the scanning angle .theta.
of the radar unit 120 meets the following condition:
where L is the relative distance between the vehicle 54 and the
target 56, and W is a width of the target 56.
AS previously described, the value of .theta.vh (which is 1/2 of
the reference range value) corresponds to the beam scanning range
of the radar unit 120 for 1/2 of the width W of the target.
FIG. 24 shows a case in which the vehicle 54 and the target 56 are
running in the same lane along a curved path with a relative
distance L between the vehicle 54 and the target 56. A radius R of
curvature of the curved path and the relative distance of the
target 56 are determined by the radar apparatus of the present
embodiment. The determination as to whether the target 56 is in the
roadway lane which is the same as that of the vehicle 54 is
performed depending on whether the center scanning angle .theta.c
of the radar unit 120 for the center of the target 56 meets the
following conditions:
where K is a predetermined coefficient of the radar apparatus.
Referring back to FIG. 22, when the result at the step S40 is
affirmative, it is determined that the target 56 in the roadway
lane which is the same as that of the vehicle 54 has been detected
at the preceding cycle of the control procedure. At this time, step
S41 is performed next.
On the other hand, when the result at the step S40 is negative, it
is determined that the target 56 in the roadway lane which is the
same as that of the vehicle 54 has not been detected at the
preceding cycle of the control procedure. At this time, step S46 is
performed next, and steps S41 through S45 are not performed.
Step S41 detects whether the recognition data related to the target
56 in the scanning range of the radar unit 120 in which the target
56 has been detected at the preceding cycle is detected at the
present cycle.
When no recognition data related to the target 56 in the scanning
range of the radar unit 120 is detected at the present cycle (the
result at the step S41 is negative), it is determined that the
target 56, previously detected to be in the roadway lane of the
vehicle 54, has been moved to a different roadway lane. At this
time, step S46 is performed next, and steps S42 through S45 are not
performed.
When the result at the step S41 is affirmative, it is determined
that the recognition data related to the target 56 in the scanning
range of the radar unit 120 in which the target 56 has been
detected at the preceding cycle is detected at the present cycle.
At this time, step S42 is performed next.
Step S42 detects whether the relative distance L of the target 56
presently determined at the present cycle is approximate to the
relative distance L of the target 56 previously determined at the
preceding cycle. As described above, the control procedure of FIG.
22 is performed for every 100 msec. When the relative distance L of
the target 56 presently determined at the present cycle is
considerably different from the relative distance L of the target
56 previously determined at the preceding cycle, it is determined
that the recognition data of the target 56 presently detected at
the present cycle is defective.
Therefore, when the result at the step S42 is negative, it is
determined that the recognition data of the target 56 presently
detected at the present cycle is defective. At this time, step S46
is performed next, and steps S43 through S45 are not performed.
On the other hand, when the result at the step S42 is affirmative,
it is determined that the relative distance L of the target 56
presently determined at the present cycle is correct. At this time,
step S43 is performed next. Step S43 detects whether the range of
the scanning angle of the radar unit 120 presently detected at the
present cycle is considerably greater than the range of the
scanning angle of the radar unit 120 previously detected at the
preceding cycle.
When the result of the step S43 is affirmative, it is determined
that another target has presently moved into or approached a
roadway lane adjacent to the roadway lane of the target 56 in the
range of the scanning angle of the radar unit 120 previously
detected at the preceding cycle. Because of the above change, a
group of plots of the data of the received reflection signals
related to the other target and a group of plots of the data of the
received reflection signals related to the target 56 may gather in
a single area in which the relative distances L are substantially
the same. At this time, step S44 is performed next.
Step S44 reads out the group of the plots of the data of the
received reflection signals related to the target 56 in the range
of the scanning angle previously detected preferential to that in
the range of the scanning angle presently detected. After the step
S44 is performed, step S46 is performed.
On the other hand, when the result at the step S43 is negative, it
is determined that the range of the scanning angle presently
detected at the present cycle is not considerably greater than the
range of the scanning angle previously detected at the preceding
cycle. At this time, step S45 is performed next. Step S45 reads out
the group of the plots of the data of the received reflection
signals in the range of the scanning angle presently detected at
the present cycle. After the step S45 is performed, step S46 is
performed.
Step S46 reads out the group of the plots of the data of the
received reflection signals related to another target which is
detected to be in another roadway lane which is different from the
roadway lane of the vehicle 54.
After the step S46 is performed, step S47 is performed. Step S47
stores all the groups of the plots of the read-out data of the
received reflection signals in a memory of the target recognition
part 136 of the radar control unit (ECU) 110.
After the step S47 is performed, step S48 is performed. Step S48
calculates the values of the relative distances L and the relative
velocities Vr related to the targets from the stored data for each
of the groups of the plots.
In the above-described embodiment, it is possible to accurately
detect individual targets in a forward direction of the vehicle by
separately processing the data of received reflection signals
related to one target from the data related to another even when
two or more targets are adjacent to each other and running in
parallel in the forward direction of the vehicle.
Next, FIG. 25 shows a radar apparatus in a further embodiment of
the present invention. In FIG. 25, the elements which are the same
as corresponding elements in FIG. 11 are designated by the same
reference numerals, and a description thereof will be omitted.
Referring to FIG. 25, the radar apparatus of the present embodiment
includes a radar control unit 210 which is an electronic control
unit (ECU) for controlling the radar apparatus including the
scanning controller 122 and the radar unit 120. This radar
apparatus is installed on an automotive vehicle.
The radar control unit 210 of the present embodiment has a
construction which is essentially the same as the construction of
the radar control unit 110 shown in FIG. 12. This radar control
unit 210 comprise the scanning angle determining part 132, the
radar signal processing part 134 and the target recognition part
136 which are the same as those of the radar control unit 110
previously described with reference to FIG. 12.
The results of the detection of targets from the radar control unit
210 are supplied to the vehicle control unit (ECU) 112. Similarly
to the vehicle control unit 112 in FIG. 11, the alarm unit 126, the
brake unit 128 and the throttle valve 130 are connected to outputs
of the vehicle control unit 112 of the present embodiment. These
units provide a warning of a dangerous condition to a vehicle
operator and decelerates the vehicle for safety.
The radar apparatus of the present embodiment is characterized by
the radar control unit 210 which carries out a control procedure.
This control procedure will be described later.
The radar signal processing part 134 of the present embodiment has
a construction which is essentially the same as that of the radar
signal processing part 134 shown in FIG. 13. This radar signal
processing part 134 comprises the carrier generator 136, the
frequency modulation circuit 140, the modulation voltage generator
142, the directional coupler 144, the mixer 146, the amplifier 148,
the filter 150 and the FFT circuit 152 which are the same as those
of the radar signal processing part 134 previously described with
reference to FIG. 13.
In the present embodiment, when the spectrum level peaks of the
up-frequency and the down-frequency of the beat signals as shown in
FIGS. 15A and 15B are determined by the FFT circuit 152 of the
radar control unit 210, a pairing of the peaks FMu1 and FMd1 is
performed so that the values of the relative distance L and the
relative velocity Vr related to one target can be obtained by using
the above Equations (1)-(4). Further, a pairing of the peaks Fmu2
and FMd2 is performed, and the values of the relative distance L
and the relative velocity Vr related to another target can be
obtained by using the above Equations (1)-(4).
As previously described with reference to FIGS. 16 and 17, in the
present embodiment, the entire range of the beam scanning of the
radar unit 120 in FIG. 16 is divided into forty subsections, the
calculated values of the relative distance L and the relative
velocity Vr related to one target are obtained for each subsection
(corresponding to 2.5 msec). In the present embodiment, for every
100 msec during which the beam scanning of the radar unit 120 is
performed, forty sets of the spectrum level peaks of the
up-frequency and the down-frequency, corresponding to respective
forty scanning angles .theta., are determined by the FFT circuit
152, and forty sets of the calculated values of the relative
distance L and the relative velocity Vr related to the target are
obtained by the radar signal processing part 134. These calculated
values which are related to the respective scanning angles .theta.
are supplied from the radar signal processing part 134 to the
target recognition part 136.
FIG. 26 shows a beam scanning of the radar unit 120 to two targets
50 and 52 in the forward direction of the vehicle. The target 50 is
a fixed pole on a roadway in the forward direction of the vehicle.
The target 52 is an advancing vehicle running along the roadway in
the forward direction of the vehicle.
As described above, a set of the spectrum level peaks of the
up-frequency and the down-frequency is determined for a range of
the scanning angle .theta. corresponding to one subsection is
determined. In FIG. 26, boundary lines of each range of the
scanning angle for one subsection are indicated by solid lines, and
a pair of boundary lines of a width of electromagnetic waves for
the beam scanning directed to one subsection are indicated by
dotted lines.
In FIG. 26, when the beam radiation axis of the radar unit 120 is
moved from the leftmost boundary line to the next boundary line for
one subsection (corresponding to a 0.5.degree. change in the
scanning angle .theta.), a range of the beam scanning indicated by
"C1" is performed. Further, when the beam radiation axis of the
radar unit 120 is moved for a further 0.5.degree. change in the
scanning angle .theta., adjacent ranges of the beam scanning
indicated by "C2", "C3" and "C4" are subsequently performed. These
ranges "C1" through "C4" of the beam scanning overlap the adjacent
ones. If a target is located near a boundary line between two
adjacent ranges of the beam scanning, it is possible that the
spectrum level peaks of the up-frequency and the down-frequency
related to the same target be determined from each data of the
reflection signals detected in the two ranges of the beam
scanning.
In the beam scanning of FIG. 26, the target 50 is located near the
boundary line between the range C1 and the range C2. The spectrum
level peaks related to the target 50 are determined from each of
the data of the reflection signals detected in the range C1 and the
data of the reflection signals detected in the range C2. Further,
the target 52 is located near the boundary line between the range
C2 and the range C3, and the spectrum level peaks related to the
target 52 are determined from each of the data of the reflection
signals detected in the range C2 and the data of the reflection
signals detected in the range C3.
FIGS. 27A and 27B show spectrum levels of the up-frequency and the
down-frequency determined for the range "C1" of the beam scanning
in FIG. 26. As shown in FIG. 27A, a spectrum level peak "Su50" of
the up-frequency related to the target 50 is determined from the
data of the reflection signals for the range C1. As shown in FIG.
27B, a spectrum level peak "Sd50" of the down-frequency related to
the target 50 is determined from the data of the reflection signals
for the range C1. Since the target 50 is the fixed pole, the
relative velocity between the vehicle and the target 50 is
considerably great. The frequency of the peak Sd50 is considerably
separated from the frequency of the peak Su50.
FIGS. 28A and 28B show spectrum levels of the up-frequency and the
down-frequency determined for the range "C2" of the beam scanning
in FIG. 26. As shown in FIG. 28A, a spectrum level peak "Su52" of
the up-frequency related to the target 52 and the spectrum level
peak Su50 are determined from the data of the reflection signals
for the range C2. As shown in FIG. 28B, a spectrum level peak
"Sd52" of the down-frequency related to the target 52 and the
spectrum level peak Sd50 are determined from the data of the
reflection signals for the range C2. Since the target 52 is running
in advance of the vehicle, the relative velocity between the
vehicle and the target 52 is not considerably great. The difference
between the frequency of the peak Su52 and the frequency of the
peak Sd52 is relatively small.
FIGS. 29A and 29B show spectrum levels of the up-frequency and the
down-frequency determined for the range "C3" of the beam scanning
in FIG. 26. As shown in FIG. 29A, only the spectrum level peak Su52
of the up-frequency is determined from the data of the reflection
signals for the range C3. As shown in FIG. 27B, only the spectrum
level peak Sd52 of the down-frequency is determined from the data
of the reflection signals for the range C3.
FIGS. 30A and 30B show spectrum levels of the up-frequency and the
down-frequency determined for the range "C4" of the beam scanning
in FIG. 26. As shown, no spectrum level peak is determined from the
data of the reflection signals for the range C4.
When a single set of the spectrum level peaks of the up-frequency
and the down-frequency is determined as in the case of FIGS. 27A
and 27B or FIGS. 29A and 29B, the values of the relative distance L
and the relative velocity Vr related to the target can be easily
and accurately calculated by using the above Equations (1)-(4).
However, a plurality of sets of the spectrum level peaks of the
up-frequency and the down-frequency related to a plurality of
targets are determined as in the case of FIGS. 28A and 29B, it is
difficult to accurately calculate the values of the relative
distance L and the relative velocity Vr related to each target. In
order to easily obtain accurate values of the relative distance L
and the relative velocity Vr for each target, it is necessary to
suitably perform a pairing of the spectrum level peaks related to
the target and a pairing of the spectrum level peaks related to
another target.
In the radar control unit 210 of the present embodiment, a pairing
of the spectrum level peaks related to one target and a pairing of
the spectrum level peaks related to another target are selectively
performed based on the data of the scanning angle.
FIGS. 31A and 31B show a control procedure which is performed by
the radar control unit 210 of the radar apparatus in FIG. 25. This
control procedure is performed in order to achieve the
above-mentioned function of the radar control unit 210. The control
procedure in FIGS. 31A and 31B is started for every 100 msec needed
for one beam scanning of the radar unit 120 to be performed by
changing the scanning angle .theta. from -10.degree. to +10.degree.
or vice versa.
Referring to FIG. 31A, the radar control unit 210, at step S60,
increments a counter i (i.rarw.i+1). The counter i indicates a
specific range of the beam scanning of the radar unit 120 for one
of forty subsections. When the radar control unit 210 is in an
initial condition, the counter i is reset to zero.
After the step S60 is performed, step S61 detects whether the data
of the reflection signals for the range "i" indicated by the
counter i is input.
When the inputting of the data is not completed, the result at the
step S61 is negative. At this time, the step S61 is repeated until
the inputting of the data is completed.
When the result at the step S61 is affirmative, step S62 is
performed. Step S62 performs the radar signal processing of the
data of the reflection signals for the range of the beam scanning
so that the spectrum level peaks of the up-frequency and the
down-frequency for that range are determined.
After the step S62 is performed, step S63 is performed. Step S63
detects whether the number of peaks included in the spectrum level
data for one of the up-frequency and the down-frequency is greater
than one.
When the result at the step S63 is negative, step S66 is performed
and steps S64 and S65 are not performed. At this time, a single set
of the spectrum level peaks of the up-frequency and the
down-frequency can be easily and accurately determined as in the
case of FIGS. 27A and 27B or FIGS. 29A and 29B.
When the result at the step S63 is affirmative, step S64 is
performed. At this time, a plurality of sets of the spectrum level
peaks of the up-frequency and the down-frequency related to a
plurality of targets are determined as in the case of FIGS. 28A and
28B. Step S64 performs a pairing of the spectrum level peaks
related to the target and a pairing of the spectrum level peaks
related to another target on the order of the frequency of each
peak.
After the step S64 is performed, step S65 detects whether a
correlation factor of the spectrum level peaks of each set is above
a threshold value .alpha.th.
The correlation factor is determined based on the shape of the
spectrum level chart for the spectrum level peaks of each pair.
When the spectrum level peaks are related to the same target, the
correlation factor is set at a relatively great value. On the other
hand, when the spectrum level peaks are related to different
targets, the correlation factor is set at a relatively small value.
At this time, the result at the step S65 is negative.
When the result at the step S65 is affirmative, it is determined
that the pairings of the spectrum level peaks related to the
plurality of targets are suitably performed. At this time, step S66
is performed. Step S66 determines the values of the relative
distance L and the relative velocity Vr related to each target, and
stores the determined values of the relative distance L and the
relative velocity Vr of the target and the value of the counter i
(indicating the range of the beam scanning) related thereto in a
memory of the radar control unit 210.
When the result at the step S65 is negative, it is determined that
the pairings of the spectrum level peaks related to the plurality
of targets are not suitably performed. At this time, step S67 is
performed. Step S67 stores the data of the spectrum level peaks in
one of unfixed-peak areas of the memory of the radar control unit
210. In this embodiment, the stored data at the step S67 includes
the value of the counter i, the spectrum level peaks, and the
frequencies of the spectrum level peaks.
After the step S66 or the step S67 is performed, step S68 is
performed. Step S68 detects whether the value of the counter i is
above a predetermined value n. The predetermined value n indicates
the final range of the beam scanning of the radar unit 120.
When the result at the step S68 is negative, it is determined that
the inputting of the data of reflection signals for all the ranges
of the beam scanning is not completed. At this time, the above
steps S60 through S67 are repeated until the inputting of all the
data is completed.
When the result at the step S68 is affirmative, it is determined
that the inputting of all the data is completed. At this time, step
S69 is performed. Step S69 resets the counter i to zero (i.rarw.0).
After the step S69 is performed, step S70 in FIG. 31B is
performed.
Referring to FIG. 31B, step S70 sets a counter j at an unfixed-peak
area number. This unfixed-peak area number indicates the
unfixed-peak area of the memory of the radar control unit 210 in
which the data of the spectrum level peaks is stored at the step
S67. The value of the counter j at the step S70 indicates a
specific one of the unfixed-peak areas of the memory of the radar
control unit 210.
After the step S70 is performed, step S71 sets a counter k at the
value (j-1).
Step S72 detects whether the data of the spectrum level peaks
stored in the unfixed-peak area indicated by the value of the
counter k has been fixed to determine the values of the relative
distance and the relative velocity.
When the result at the step S72 is negative, it is determined that
the data of the spectrum level peaks stored in the area "k" has not
been fixed. At this time, step S73 is performed. Step S73 detects
whether the value of the counter k is smaller than the value of the
counter j.
When the result at the step S73 is affirmative (k<j), step S74
decrements the counter k (k.rarw.k-1). On the other hand, when the
result at the step S73 is negative (k.gtoreq.j), step S75
increments the counter k (k.rarw.k+1).
After the step S74 or the step S75 is performed, the above step S72
is repeated until it is determined that the data of the spectrum
level peaks stored in the area "k" has been fixed.
When the result at the step S72 is affirmative, it is determined
that the data of the spectrum level peaks stored in the area "k"
has been fixed. At this time, step S76 is performed. Step S76
detects whether the spectrum level peaks stored in the area "k" are
the same as those stored in an adjacent unfixed-peak area of the
memory which is adjacent to the area "k".
When the result at the step S76 is affirmative, it is determined
that the pairings of the spectrum level peaks are suitably
performed based on the peaks in the adjacent area which are the
same. At this time, step S78 is performed.
On the other hand, when the result at the step S76 is negative, it
is determined that the pairings of the spectrum level peaks in this
case cannot be suitably performed. At this time, step S77 is
performed. Step S77 sets the counter k at the value (j+1). After
the step S77 is performed, the above step S72 is repeated.
Step S78 performs the pairings of the spectrum level peaks related
to the data in the area "k" based on the peaks in the adjacent
area. Since the number of the peaks included in the data in the
area "k" is reduced, the pairings of the spectrum level peaks are
easily performed.
After the step S78 is performed, step S79 is performed. Step S79
performs the pairings of the remaining spectrum level peaks in the
data in the area "k" on the order of the frequency of each peak and
by using the correlation factor as in the steps S64 through
S67.
After the step S79 is performed, step S80 is performed. Step S80
detects whether all the data of the spectrum level peaks stored in
all the unfixed-peak areas of the memory have been fixed to
determine the values of the relative distance and the relative
velocity.
When the result at the step S80 is negative, the steps S70 through
S79 are repeated until all the data of the spectrum level peaks are
fixed. On the other hand, when the result at the step S80 is
affirmative, the control procedure of the radar control unit 210 at
the present cycle ends.
It is possible that the radar apparatus of the present embodiment
easily and accurately detects individual targets in a forward
direction of the vehicle by separately performing a pairing of the
data of received reflection signals related to one target and a
pairing of the data of received reflection signals related to
another target when a plurality of targets in the forward direction
of the vehicle are detected. By performing the steps S70 through
S78, the radar control unit 210 can separately perform the pairings
of the spectrum level peaks in the unfixed-peak areas related to
the plurality of targets, so that the relative distance and the
relative velocity of each of the targets can be easily and
accurately determined.
Further, the present invention is not limited to the
above-described embodiments, and variations and modifications may
be made according to the present invention.
* * * * *